Good question. A couple options you could use to approach this:

1. You could look for other designers who are also looking to do personal projects and collaborate with them through the project (shows design collaboration skills)

2. You could look for engineers, user researchers, etc. to develop your idea (shows you can interact with cross functional teammates)

3. If you didn’t have any experience working with cross functional members, you can articulate in your presentation how you would have interacted with them if you had team members or resources. (ie For this project I didn't have a user researcher, but if I did we would have conducted a large scale study testing xyz)